Adeno-associated virus (AAV) is a small, defective, human DNA virus which requires co-infection with adenovirus in order to multiply. AAV is an unusual virus because there are two types of virions. One virion type contains the plus DNA strand and the other type contains the minus strand. When DNA is released from the virions, the complementary strands from different particles anneal to form double-stranded DNA. We have characterized the purified mature virion DNA and have found that it is a linear single polynucleotide chain whose nucleotide sequence contains two or more permutations all of whose start points occur within a limited region representing less than 6 percent of the length of the genome. Additionally, the DNA contains terminal nucleotide sequences which have properties consistent with both natural and inverted nucleotide sequence repetitions. Because these are undoubtedly involved in the replication of the DNA we plan to determine the actual nucleotide sequences. We will also study the production of specific DNA fragments using bacterial restriction enzymes to digest DNA isolated from virions. Replicating DNA will be isolated from infected cells and physically characterized. AAV can also latently infect human cells. We will try to quantitate the amount of AAV DNA in the latently infected cells using reannealing kinetics.